Influence of height on the nerve conduction study parameters of the peripheral nerves

INTRODUCTION BACKGROUND: Nerve conduction studies (NCS) which assess peripheral nerve functions and their parameters, are known to vary with anthropometric measurements. OBJECTIVE: To study the effect of height on the NCS variables in the peripheral nerves of the limbs. SETTINGS AND DESIGNS: Department of Physiology, normative. METHODS AND MATERIAL: This study was done on 34 (age: 31.24±11.57 years) consenting, healthy adults of either sex. The anthropometric factors (height, weight and BMI); the compound muscle action potential (CMAP) and the sensory nerve action potential (SNAP) were recorded by using standard techniques. STATISTICAL ANALYSIS: The correlation of height with the NCS variables was analyzed by using the Pearson’s correlation test. RESULTS: After the adjustment of other anthropometric factors, height (158.5±10.21cm) showed a positive correlation with the CMAP duration of all the motor nerves: right median (r=0.734, p<0.001), left median (r=0.422, p<0.05), right ulnar (r=0.561, p<0.01), left ulnar (r=0.661, p<0.001), right tibial (r=0.372, p<0.05) THAKUR D, JHA S, PANDEY NK, JHA CB, BAJAJ BK, PAUDEL BH and the left tibial (r=0.353, p<0.05). The CMAP amplitudes and the latencies were also positively correlated, with the exception of the ulnar and the right radial nerves. A positive correlation with the Fwave latencies were seen in all the nerves, except in the left common peroneal nerve. However, a negative correlation was seen with the SNAP amplitude of the right sural nerve (r= -0.442, p<0.01) and the conduction velocity of the ulnar motor nerves: right ulnar (r= -0.536, p<0.01) and left ulnar (r= -0.430, p<0.05). The SNAP duration and the conduction velocity did not show any correlation with height. CONCLUSION: Height showed a significant correlation with the NCS parameters of the motor and few sensory nerves. Diagnostic conclusions which are made from the nerve conduction data without making corrections for the height may be invalid in patients who are taller and shorter than the average individuals. This must be also be considered while developing standard/reference normative data for different nerves. Nerve conduction studies (NCS) are performed to diagnose the disorders of the peripheral nervous system [1], [2]. These enable the clinicians to differentiate the two major groups of peripheral diseases: demyelination and axonal degeneration [3]. These also help in localizing the site of the lesions [4], [5]. NCS consist primarily of the assessment of three types of nerves: motor, sensory and mixed. Motor NCS include the assessment of the compound muscle action potential (CMAP), whereas sensory NCS include the assessment of the sensory nerve action potentials (SNAP) of the accessible peripheral nerves in the upper and lower limbs. The median, ulnar, radial, common peroneal, tibial and the sural nerves are the commonly examined nerves. The commonly measured parameters of the CMAP include latency, amplitude, duration, conduction velocity and late response, e.g., F-waves. Similarly, for SNAP, latency, amplitude and conduction velocity are routinely measured [2]. These parameters are known to vary with demographic profile, anthropometric measurements such as height, BMI, etc of the population which is studied and the laboratory conditions of the test1. Many studies have been done previously to evaluate the influence of the anthropometric factors such as age, height and body mass index on the nerve velocities [6], [7], [8]. However, a majority of these studies were based on the western population. Therefore, this study was designed to find the effect of height on the NCS parameters of the peripheral nerves in the upper and lower limbs among our healthy population. OBJECTIVE To study the correlation of height with the NCS variables of the peripheral nerves of the upper and lower limbs. METHODS This study was done in 34 (age: 31.24±11.57 years) healthy adults of either sex in the Neurophysiology lab of the Department of Physiology, BPKIHS, Nepal. An informed written consent was taken from the volunteers and they were screened for any history of drugs/alcohol intake or medical illness which was likely to affect the nerve conduction study parameters on the basis of clinical history and physical examination, including a detailed neurological assessment. The room temperature of the laboratory was maintained at the thermo neutral zone i.e. 26±2 degree celsius. Further, the subjects were made comfortable with the laboratory set up and conditions and were advised to relax completely during the recording. The CMAP and SNAP were recorded under standard laboratory conditions by using a Nihon Kohden machine (NM-420S; H36, Japan). The recorded anthropometric and nerve conduction study variables [1], [2] The Anthropometric factors: age, sex, height, weight, body mass index and body surface were recorded.